Disclosed in JP2004-259151A is a collision avoidance control system for a vehicle, which executes a collision avoidance control for avoiding a collision of the vehicle against a target object while accurately determining a possibility of the collision and calculating a control amount for avoiding the collision with less calculation in a manner where the collision avoidance control system selects the target object (e.g. a vehicle traveling ahead of the subject vehicle having the collision avoidance control system) to be subjected to the control on the basis of an information received from a radar sensor, each electronic control unit (ECU) and the like, obtains a collision avoidance deceleration necessary for decelerating the subject vehicle so that a relative speed between the target object and the subject vehicle becomes zero (0), by which the collision of the subject vehicle against the target object is avoidable, and generates a braking force based on the collision avoidance deceleration.
Disclosed in JPH11-211492A is a road information recognition system that calculates a first road information on the basis of a data stored within a navigation device, calculates a second road information on the basis of a data obtained by an image capture device, and compares a curvature radius of a curve and the like based on the first road information with a curvature radius of the curve and the like based on the second road information. Then, the road information recognition system disclosed in JPH11-211492A sets the curvature radius of the curve and the like in a case where the curvature radius of the curve based on the first road information, the curvature radius of the curve based on the second road information and the like satisfy predetermined conditions in order to detect a detailed, accurate and reliable information relating to a road extending ahead of a vehicle. Furthermore, the road information recognition system disclosed in JPH11-211492A executes a braking operation and the like on the basis of the information relating to the curvature radius of the curve and the like in a case where the vehicle needs to be forcibly decelerated.
Disclosed in JP2005-289205A is a motion control device for a vehicle, which is configured so as to select either a deceleration control (an avoidance control) or a turning control (a stabilization control) depending on a driving situation in order to restrict an interference in the control occurring when the turning control (the stabilization control) for restricting an understeering tendency and an oversteering tendency is started while the deceleration control (the avoidance control) is being executed. More specifically, in the deceleration control (the avoidance control), a deceleration control quantity for decelerating the vehicle is calculated and a wheel braking force is controlled on the basis of the deceleration control quantity. In the turning control (the stabilization control), a second deceleration control quantity for decelerating the vehicle is calculated and the wheel braking force is controlled on the basis of the second deceleration control quantity in a case where the understeering tendency occurs at the vehicle (i.e. an understeering restriction control). On the other hand, in a case where the oversteering tendency occurs at the vehicle, a yaw moment control quantity for generating a yaw moment at the vehicle in a turning outer direction is calculated and the wheel braking force is controlled on the basis of the yaw moment control quantity (i.e. an oversteering restriction control). Then, in the case where the understeering tendency is occurring at the vehicle, either the deceleration control quantity of the deceleration control (the avoidance control) or the second deceleration control quantity of the turning control (the stabilization control) having a greater value is selected, so that the wheel braking force is controlled on the basis of the deceleration control quantity of the deceleration control or the second deceleration control quantity having the greater value in order to avoid an occurrence of the interference in the controls between the deceleration control (the avoidance control) and the turning control (the stabilization control). On the other hand, in the case where the oversteering tendency is occurring at the vehicle, the wheel braking force is controlled on the basis of the yaw moment control quantity of the turning control (the stabilization control).
The collision avoidance control for avoiding the collision of the vehicle against the target object existing in front of the subject vehicle (e.g. the vehicle traveling in front of the subject vehicle) on the basis of an information relating to a distance between the subject vehicle and the target object (JP2004-259151A) and a departure avoidance control for decelerating the vehicle on the basis of the information relating to the curve of the road existing ahead of the vehicle so that the vehicle does not depart from the curve (JPH11-211492A) are referred to as an emergency avoidance control (which is also referred to simply as an avoidance control) for avoiding an emergency state of the vehicle by decelerating the vehicle. As disclosed in JP2005-289205A, in the case where either one of the avoidance control and the stabilization control is selected when the execution conditions of the avoidance control and the stabilization control are both satisfied and then the control (the braking control) is simply switched between the avoidance control and the stabilization control, the vehicle may not be sufficiently decelerated, or the vehicle may not be sufficiently stabilized.
More specifically, the following drawbacks may occur. Firstly, a case where the understeering tendency occurs at the vehicle while the deceleration control (the avoidance control) is being executed and a start of the turning control (the stabilization control) is determined will be considered below. In this case, the understeering tendency of the vehicle needs to be resolved. However, in a case where the deceleration control quantity of the deceleration control is greater than the second deceleration control quantity of the turning control and the deceleration control quantity of the deceleration control is selected, the deceleration control is kept being executed. As a result, the understeering tendency of the vehicle is not resolved, because the understeering restriction control is not executed.
Secondly, a case where the oversteering tendency occurs at the vehicle while the deceleration control (the avoidance control) is being executed and a start of the turning control (the stabilization control) is determined will be considered below. In this case, the control quantity used for the control of the wheel braking force is suddenly switched from the deceleration control quantity of the deceleration control to the yaw moment control quantity of the turning control. As a result, a sudden change may occur at a total wheel braking force when the control is switched. In this case, a driver may feel discomfort.
A need thus exists to provide a motion control device for a vehicle in which an interference in controls between an emergency avoidance control (an avoidance control) for avoiding an emergency state of the vehicle (e.g. a departure of the vehicle from a road, a collision of the vehicle against a vehicle traveling ahead of the subject vehicle and the like) and a stabilization control for appropriately maintaining a steering characteristic of the vehicle is avoided in order to achieve a smooth braking control. Furthermore, a need thus exists to provide the motion control device for the vehicle in which the emergency avoidance control and the stabilization control are achieved with a simple system architecture (e.g. a brake configuration that does require to provide a brake hydraulic pressure sensor at each wheel and the like).